…there are five types of adrenergic receptors (receptors binding epinephrine): α1, α2, β1, β2, and β3. These adrenoceptors are found in different combinations in various cells throughout the body. Activation of α1- adrenoceptors in arterioles causes blood-vessel constriction, whereas stimulation of α2 autoreceptors (receptors located in sympathetic presynaptic nerve endings)…

interaction with drugs

…is said to be an adrenoceptor. Ahlquist called the two kinds of adrenoceptor alpha (α) and beta (β). This theory was confirmed when Sir James Black developed a new type of drug that was selective for the β-adrenoceptor.